Central composite design and optimization of selected stir casting parameters on flexural strength and fracture toughness mTiO2p/Al 7075 composites

Abstract

Ceramic particulate like titanium dioxide play major role in enhancement of properties of aluminium composites for high strength-low weight applications. The major process used in the dispersion of the particles in the melt is the stir casting route. There is need for incremental studies on the modelling and optimization of the procedure. This study reports the influence of stirring temperature, speed, and time on the flexural strength and fracture toughness of Al 7075 reinforced with 10 wt% micro titanium dioxide of average size 13 µm, produced via stir casting. Central composite design (CCD) was employed in the design of experiment and specimen were produced according to the experimental runs. The result of the analysis of variance (ANOVA) showed that the parameters contributed significantly to the responses and satisfactory models were obtained for the properties under investigation. The interaction between the parameters revealed that increasing speed and time ensued improvement in the properties. An uptrend in temperature was observed to enhance the flexural strength but reduce fracture toughness. Response surface optimization revealed combined parameters for optimal performance as 643.4 ˚C, 423 rpm, and 30 mins for temperature, speed and time respectively yielding 470.4 MPa and 34.7 MPa.m1/2 for flexural strength and fracture toughness in that order. Model validation experiment was carried out using the combined parameters and deviation of −0.024 and + 0.014 were obtained for the flexural strength and fracture toughness respectivelyectively. Since the values were less than 0.05, the models were concluded to be statistically fit for resposne prediction.